For some time now, Twitter has been working on a new API: the Twitter Streaming API. The idea behind it is to allow third-party Twitter clients to receive continuous tweet updates in realtime. As developer advocate Taylor Singletary notes today on the Twitter Development Talk Google Group, limited testing of this new feature (also called “User Streams”) for desktop clients has now begun.

Currently, TweetDeck and Echofon, two popular Twitter desktop clients, have access to the new API for testing. Singletary notes that not all users of these clients will see this new tech in action at first. Instead, there will be a more gradual roll-out with each app. Once that occurs, Twitter will start opening up the Streaming API to other clients as well.

While the feature is very cool and makes third-party clients much more interesting, the Streaming API also helps Twitter significantly. As Singletary notes, “The transition to User Streams should return considerable capacity to the
REST and Search APIs, increasing stability for Twitter users & developers alike.” With their recent scaling problems, one of the aspects hurt the most by limits Twitter had to impose is the API. Services like TweetDeck and Seesmic rely heavily on the Search API for their various windows — so obviously, this was a problem. The Streaming API should alleviate that quite a bit.

And there’s more. Singletary notes that:

Additionally, several interesting new event types are available: Favoriting, retweeting, following, and list additions are also streamed along with direct messages, mentions, the user timeline and the home timeline.

Again, all of this should help ease strain on the rest of Twitter’s APIs. The only question is: how long will it take to roll-out in a meaningful way? Twitter says that an open beta is tentatively scheduled for Q3 or Q4 of 2010.

At the end of the message, Singletary also hints at a new API product called Site Streams:

Application developers needing to consume multiple, simultaneous user streams will be served by an upcoming Streaming API product called Site Streams. Stay tuned for more information on that when we’re ready.